1. Technical Field
The present invention relates to methods for manufacturing semiconductor devices and, more particularly, to a lithography method for preventing lithographic exposure of a periphery region of a semiconductor wafer.
2. Description of Related Art
Photolithography is a commonly used technique in the manufacture of semiconductor devices, which utilizes patterns to define regions on a silicon substrate. More specifically, with photolithography, a photoresist layer is formed, for example, on a substrate such as a silicon wafer, and then the resist layer is covered with a mask or reticle containing a pattern. The mask is exposed to radiation such as ultraviolet light (UV), X-ray, electron beam, and the like, which is transmitted through the transparent areas of the mask to cause a chemical reaction in corresponding regions of the photoresist.
There are various exposure apparatuses that may be used for photolithography. For example, a projection exposure apparatus, which is well-known in the art, is generally used, in which an image of a pattern formed on a reticle is transferred via a projection optical system onto, e.g., a wafer substrate applied with a photosensitive material such as photoresist on its surface. A reduction projection exposure apparatus (so-called stepper) based on the so-called xe2x80x9cstep-and-repeatxe2x80x9d system is predominantly used as the projection exposure apparatus, in which a sensitive substrate is placed on a substrate stage that can be moved in two-dimensions. The sensitive substrate is moved in a stepwise manner (subjected to stepping) by using the substrate stage to repeat the operation for successively exposing respective shot areas on the sensitive substrate with the image of the pattern formed on the reticle.
Depending on the application, several resist types may be used. For example, with a negative type photoresist, the radiation impacted areas of the photoresist become insoluble in a developing solvent. For example, the radiation can initiate cross-linking, chain growth, photocondensation, or other such reaction to cause a chemical change in the photoresist. On the other hand, with a positive type photoresist, the radiation impacted areas become more soluble in a developing solvent. For example, the radiation can cause photodegradation of the photoresist molecular structure.
After radiation exposure, the photoresist is developed by exposure to a developing solvent which washes away the soluble portions of the photoresist, thereby forming a resist pattern. The resist pattern can be used for protecting the substrate during, e.g., etch or ion implantation. For example, an etching process can be conducted wherein the substrate is exposed to, e.g., an acid in a wet etch process, or an ion beam in a dry etch process, wherein the pattern can be used to form deep trenches by performing a deep trench mask opening (DTMO) process and a deep trench (DT) etching process. The areas of the substrate that are covered by the resist pattern remain unetched. The remaining photoresist is removed by a suitable solvent or other conventional removal methods, leaving the substrate with a pattern etched therein.
One disadvantage associated with the manufacture of semiconductor devices is the formation of xe2x80x9cblack siliconxe2x80x9d at the wafer periphery. As is known in the art, xe2x80x9cblack siliconxe2x80x9d may be formed for various reasons including, for example, lithographic exposure of the wafer edge. In particular, the black silicon is generally formed at the edge of the wafer due to uneven erosion of the photoresist layer, and it causes problems such as considerable contamination on the process and exposure tools (e.g., ion implanter), as well as a reduction in exposure resolution.
FIG. 1 is an exemplary schematic sectional side view of a wafer edge illustrating black silicon formation during trench etching process. FIG. 1 illustrates a silicon wafer 1 having a mask pattern 2 (e.g., oxide film) formed thereon for selectively etching the silicon wafer 1 to form trenches 3. During trench etching, the silicon at a periphery region 4 of the wafer 1 is widely exposed causing the formation of black silicon 5. During subsequent wafer processing, the projecting portions of the black silicon 5 can break down and become particles. These particles can cause a myriad of problems in manufacturing process, such as electrical insulation defects, which lowers the manufacturing yield, as well as the problems mentioned above such as tool contamination.
Methods for preventing the formation of xe2x80x9cblack siliconxe2x80x9d are described, for example, in U.S. Pat. No. 6,291,315, issued to Nakayama et al., entitled xe2x80x9cMethod for Etching Trench in Manufacturing Semiconductor Devicesxe2x80x9d. Briefly, one method disclosed in Nakayama for preventing formation of black silicon involves forming a thick oxide film in the peripheral region of a semiconductor wafer which functions as an insulating film for etching prevention when trenches are formed. In other words, during a reactive ion etching process, no silicon will be exposed in a region (e.g., periphery region) other than the region of the trench formation, thereby preventing formation of the black silicon on the wafer periphery.
Conventional methods for preventing formation of black silicon (such as the method described above) add complexity to the manufacturing process as they require additional complex steps, e.g., forming an oxide film layer at wafer periphery, in addition to typical photolithography and other semiconductor manufacturing processes.
Therefore, a need exists for a simplified method for preventing or mitigating the formation of black silicon on the periphery of a semiconductor wafer during the fabrication of semiconductor devices.
It is an object of the present invention to provide a lithography method for use in the manufacture of semiconductor devices, which prevents lithographic exposure of a periphery region or edge region of a semiconductor wafer.
It is another object of the present invention to provide a lithography method for use in the manufacture of semiconductor devices, which prevents the formation of black silicon in a patterned region on the periphery region of a semiconductor wafer as a result of, e.g., a deep trench manufacturing process.
According to one aspect of the present invention, a method for preventing lithographic exposure of a periphery region of a semiconductor wafer comprises applying a layer of photoresist on a semiconductor wafer, and then treating the photoresist that covers a peripheral region of the semiconductor wafer with a solution that prevents the treated photoresist from dissolving during a development process due to radiation exposure of the treated photoresist.
In another aspect of the invention, a method for preventing the formation of black silicon in a patterned region on a periphery of a semiconductor wafer comprises applying a layer of photoresist on a semiconductor wafer and applying a solution to the photoresist on a peripheral region of the semiconductor wafer. When the layer of photoresist is exposed to radiation, the solution prevents photochemical changes from occurring in the photoresist on the peripheral region of the semiconductor wafer as a result of the radiation exposure. When developing the photoresist to form a pattern, the solution prevents the exposed photoresist on the peripheral region of the semiconductor wafer from being dissolved by a developing agent. When an etch process is performed on an exposed portion of the semiconductor wafer, the photoresist on the peripheral region of the semiconductor wafer prevents widespread erosion of the substrate and prevents the formation of black silicon on the patterned region as a result of etching.
In another aspect of the invention, a lithography process comprises applying a layer of positive photoresist on a semiconductor wafer, and applying a solution to the positive photoresist that covers a peripheral region of the semiconductor wafer. Upon radiation exposure of the layer of photoresist, the solution prevents photochemical changes from occurring in the positive photoresist that covers the peripheral region of the semiconductor wafer due to radiation exposure. During development of the photoresist to form a resist pattern, the solution prevents exposed positive photoresist that covers the peripheral region of the semiconductor wafer from being dissolved by a developing agent.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.